1. Field of the Invention
The present invention relates to a dielectric filter and a method for manufacturing the same, and more particularly to a dielectric filter in which electrodes are formed on an open surface of a dielectric block and deposited with a thermosetting resin thereon, thereby preventing defects such as a short circuit caused by burrs generated during a subsequent tuning step, and a method for manufacturing the dielectric filter.
2. Description of the Related Art
Recently, in order to satisfy the trend toward miniaturization of mobile communication terminals, electronic components incorporated into mobile communication terminals are also required to be miniaturized.
Dielectric filters are generally used as duplexers being essential components of the mobile communication terminals. However, recently, SAW (Surface Acoustic Wave) filters or FBARs (Film Bulk Acoustic Resonators) being advantageous in terms of miniaturization have been increasingly substituted for the dielectric filters. Compared to other types of high-frequency filters, the dielectric filters are advantageous in terms of thermal stability, electrical resistance, and competitive pricing, and have a low loss factor. In view of the aforementioned characteristics of the dielectric filters, the dielectric filters have been steadily developed toward small, thin, and light characteristics, i.e., miniaturization.
Conventionally, in order to achieve the miniaturization of the dielectric filter, the dielectric filter is formed such that a dielectric block has a small thickness and an interval between resonant holes formed in the dielectric block is narrow. However, as a result, the dimensions of the dielectric filter are reduced, and simultaneously a line width of conductive patterns and an interval between the conductive patterns become narrow. Herein, the line width and the interval of the conductive patterns are factors determining electrical characteristics of the dielectric filter.
Due to the reduced line width and interval of the conductive patterns, it is difficult to trim the conductive patterns during a tuning step for adjusting resonant frequency.
Particularly, in case of an open surface of the dielectric filter, fine metal segments (hereinafter, referred to as “burr”) generated in trimming the conductive patterns are located at open areas between the conductive patterns, thereby causing electrical defects (e.g., a short circuit). These electrical defects change the resonant frequency and finally output defective products. The generation of burrs not only prevents the miniaturization of the dielectric filter, but also causes many problems in a trimming step of the conventional miniaturized dielectric filter performed by manufacturers or users.
Hereinafter, with reference to FIG. 1, the generation of burrs caused during a trimming step of conductive patterns will be described in detail.
As shown in FIG. 1, a duplexer dielectric filter 10 comprises a dielectric block 11 having resonant holes 15 passing through two opposite surfaces. An open surface 13 of the dielectric block 11 is provided with input and output terminals 21 and 23, an antenna terminal 22, and conductive patterns 25 and 29 having various shapes. The input and output terminals 21 and 23, and the antenna terminal 22 are extended to a side surface adjacent to the open surface 13 being separated from a conductive material formed on the side surface. The conductive patterns 25 and 29 provide a desired resonant frequency to the duplexer dielectric filter 10 according to sizes and intervals of the conductive patterns 25 and 29. For example, the conductive patterns 25 formed on the open surface 13 around the resonant holes 15 and connected to a conductive material deposited within the resonant holes 15 form loading capacitances between the conductive material formed on the side surfaces of the dielectric block 11 and coupling capacitances between the neighboring resonators.
After forming the conductive patterns 25 and 29, the dielectric block 11 is fired. During the firing step, the dielectric constant of the dielectric block 11 is changed, and thus the resonant frequency of the dielectric filter 10 is changed. Therefore, a tuning step for correcting this change of resonant frequency is required. On the other hand, the resonant frequency of the dielectric filter 10 may be intentionally changed according to users' demands.
As aforementioned, after producing the final products, manufacturers or users perform a turning step for trimming the conductive patterns formed on the open surface of the dielectric block so as to form a desired resonant frequency.
However, as shown in FIG. 1, in the trimming step, when a part 25a of the conductive patterns 25 formed around the resonant holes 15 is removed, a metal segment 25a′ is cut from the part 25a and disposed on an area of the open surface, thereby causing unintentional electrical defects. Particularly, as shown in the drawing, in case the metal segment 25a is disposed between the separated patterns 25 and 29, the metal segment 25a′ causes a short circuit therebetween. The short circuit may cause a fatal defect to the products.
The aforementioned problem is more severe in a miniaturized dielectric filter. Further, as the conductive patterns of the dielectric block become narrower, that is, as the dielectric block become smaller, the defect rate generated by the metal segments increases and limits the miniaturization of the dielectric filter.